#ifndef BOOST_PP_IS_ITERATING | |
/////////////////////////////////////////////////////////////////////////////// | |
/// \file when.hpp | |
/// Definition of when transform. | |
// | |
// Copyright 2008 Eric Niebler. Distributed under the Boost | |
// Software License, Version 1.0. (See accompanying file | |
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
#ifndef BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007 | |
#define BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007 | |
#include <boost/preprocessor/cat.hpp> | |
#include <boost/preprocessor/repetition/enum_params.hpp> | |
#include <boost/preprocessor/repetition/enum_trailing_params.hpp> | |
#include <boost/preprocessor/iteration/iterate.hpp> | |
#include <boost/mpl/at.hpp> | |
#include <boost/mpl/if.hpp> | |
#include <boost/mpl/map.hpp> | |
#include <boost/proto/proto_fwd.hpp> | |
#include <boost/proto/traits.hpp> | |
#include <boost/proto/transform/call.hpp> | |
#include <boost/proto/transform/make.hpp> | |
#include <boost/proto/transform/impl.hpp> | |
namespace boost { namespace proto | |
{ | |
/// \brief A grammar element and a PrimitiveTransform that associates | |
/// a transform with the grammar. | |
/// | |
/// Use <tt>when\<\></tt> to override a grammar's default transform | |
/// with a custom transform. It is for used when composing larger | |
/// transforms by associating smaller transforms with individual | |
/// rules in your grammar, as in the following transform which | |
/// counts the number of terminals in an expression. | |
/// | |
/// \code | |
/// // Count the terminals in an expression tree. | |
/// // Must be invoked with initial state == mpl::int_<0>(). | |
/// struct CountLeaves | |
/// : or_< | |
/// when<terminal<_>, mpl::next<_state>()> | |
/// , otherwise<fold<_, _state, CountLeaves> > | |
/// > | |
/// {}; | |
/// \endcode | |
/// | |
/// In <tt>when\<G, T\></tt>, when \c T is a class type it is a | |
/// PrimitiveTransform and the following equivalencies hold: | |
/// | |
/// <tt>boost::result_of\<when\<G,T\>(E,S,V)\>::type</tt> is the same as | |
/// <tt>boost::result_of\<T(E,S,V)\>::type</tt>. | |
/// | |
/// <tt>when\<G,T\>()(e,s,d)</tt> is the same as | |
/// <tt>T()(e,s,d)</tt>. | |
template<typename Grammar, typename PrimitiveTransform /*= Grammar*/> | |
struct when | |
: PrimitiveTransform | |
{ | |
typedef Grammar first; | |
typedef PrimitiveTransform second; | |
typedef typename Grammar::proto_grammar proto_grammar; | |
}; | |
/// \brief A specialization that treats function pointer Transforms as | |
/// if they were function type Transforms. | |
/// | |
/// This specialization requires that \c Fun is actually a function type. | |
/// | |
/// This specialization is required for nested transforms such as | |
/// <tt>when\<G, T0(T1(_))\></tt>. In C++, functions that are used as | |
/// parameters to other functions automatically decay to funtion | |
/// pointer types. In other words, the type <tt>T0(T1(_))</tt> is | |
/// indistinguishable from <tt>T0(T1(*)(_))</tt>. This specialization | |
/// is required to handle these nested function pointer type transforms | |
/// properly. | |
template<typename Grammar, typename Fun> | |
struct when<Grammar, Fun *> | |
: when<Grammar, Fun> | |
{}; | |
/// \brief Syntactic sugar for <tt>when\<_, Fun\></tt>, for use | |
/// in grammars to handle all the cases not yet handled. | |
/// | |
/// Use <tt>otherwise\<T\></tt> in your grammars as a synonym for | |
/// <tt>when\<_, T\></tt> as in the following transform which | |
/// counts the number of terminals in an expression. | |
/// | |
/// \code | |
/// // Count the terminals in an expression tree. | |
/// // Must be invoked with initial state == mpl::int_<0>(). | |
/// struct CountLeaves | |
/// : or_< | |
/// when<terminal<_>, mpl::next<_state>()> | |
/// , otherwise<fold<_, _state, CountLeaves> > | |
/// > | |
/// {}; | |
/// \endcode | |
template<typename Fun> | |
struct otherwise | |
: when<_, Fun> | |
{}; | |
/// \brief This specialization uses the Data parameter as a collection | |
/// of transforms that can be indexed by the specified rule. | |
/// | |
/// Use <tt>when\<T, external_transform\></tt> in your code when you would like | |
/// to define a grammar once and use it to evaluate expressions with | |
/// many different sets of transforms. The transforms are found by | |
/// using the Data parameter as a map from rules to transforms. | |
/// | |
/// See \c action_map for an example. | |
template<typename Grammar> | |
struct when<Grammar, external_transform> | |
: proto::transform<when<Grammar, external_transform> > | |
{ | |
typedef Grammar first; | |
typedef external_transform second; | |
typedef typename Grammar::proto_grammar proto_grammar; | |
template<typename Expr, typename State, typename Data> | |
struct impl | |
: Data::template when<Grammar>::template impl<Expr, State, Data> | |
{}; | |
template<typename Expr, typename State, typename Data> | |
struct impl<Expr, State, Data &> | |
: Data::template when<Grammar>::template impl<Expr, State, Data &> | |
{}; | |
}; | |
/// \brief For defining a map of Rule/Transform pairs for use with | |
/// <tt>when\<T, external_transform\></tt> to make transforms external to the grammar | |
/// | |
/// The following code defines a grammar with a couple of external transforms. | |
/// It also defines an action_map that maps from rules to transforms. It then | |
/// passes that transforms map at the Data parameter to the grammar. In this way, | |
/// the behavior of the grammar can be modified post-hoc by passing a different | |
/// action_map. | |
/// | |
/// \code | |
/// struct int_terminal | |
/// : proto::terminal<int> | |
/// {}; | |
/// | |
/// struct char_terminal | |
/// : proto::terminal<char> | |
/// {}; | |
/// | |
/// struct my_grammar | |
/// : proto::or_< | |
/// proto::when< int_terminal, proto::external_transform > | |
/// , proto::when< char_terminal, proto::external_transform > | |
/// , proto::when< | |
/// proto::plus< my_grammar, my_grammar > | |
/// , proto::fold< _, int(), my_grammar > | |
/// > | |
/// > | |
/// {}; | |
/// | |
/// struct my_transforms | |
/// : proto::external_transforms< | |
/// proto::when<int_terminal, print(proto::_value)> | |
/// , proto::when<char_terminal, print(proto::_value)> | |
/// > | |
/// {}; | |
/// | |
/// proto::literal<int> i(1); | |
/// proto::literal<char> c('a'); | |
/// my_transforms trx; | |
/// | |
/// // Evaluate "i+c" using my_grammar with the specified transforms: | |
/// my_grammar()(i + c, 0, trx); | |
/// \endcode | |
template<BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_MPL_LIMIT_MAP_SIZE, typename T, mpl::na)> | |
struct external_transforms | |
{ | |
typedef mpl::map<BOOST_PP_ENUM_PARAMS(BOOST_MPL_LIMIT_MAP_SIZE, T)> map_type; | |
template<typename Rule> | |
struct when | |
: proto::when<_, typename mpl::at<map_type, Rule>::type> | |
{}; | |
}; | |
#define BOOST_PP_ITERATION_PARAMS_1 (3, (0, BOOST_PROTO_MAX_ARITY, <boost/proto/transform/when.hpp>)) | |
#include BOOST_PP_ITERATE() | |
/// INTERNAL ONLY | |
/// | |
template<typename Grammar, typename Transform> | |
struct is_callable<when<Grammar, Transform> > | |
: mpl::true_ | |
{}; | |
}} // namespace boost::proto | |
#endif | |
#else | |
#define N BOOST_PP_ITERATION() | |
/// \brief A grammar element and a PrimitiveTransform that associates | |
/// a transform with the grammar. | |
/// | |
/// Use <tt>when\<\></tt> to override a grammar's default transform | |
/// with a custom transform. It is for used when composing larger | |
/// transforms by associating smaller transforms with individual | |
/// rules in your grammar, as in the following transform which | |
/// counts the number of terminals in an expression. | |
/// | |
/// \code | |
/// // Count the terminals in an expression tree. | |
/// // Must be invoked with initial state == mpl::int_<0>(). | |
/// struct CountLeaves | |
/// : or_< | |
/// when<terminal<_>, mpl::next<_state>()> | |
/// , otherwise<fold<_, _state, CountLeaves> > | |
/// > | |
/// {}; | |
/// \endcode | |
/// | |
/// The <tt>when\<G, R(A0,A1,...)\></tt> form accepts either a | |
/// CallableTransform or an ObjectTransform as its second parameter. | |
/// <tt>when\<\></tt> uses <tt>is_callable\<R\>::value</tt> to | |
/// distinguish between the two, and uses <tt>call\<\></tt> to | |
/// evaluate CallableTransforms and <tt>make\<\></tt> to evaluate | |
/// ObjectTransforms. | |
template<typename Grammar, typename R BOOST_PP_ENUM_TRAILING_PARAMS(N, typename A)> | |
struct when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A))> | |
: transform<when<Grammar, R(BOOST_PP_ENUM_PARAMS(N, A))> > | |
{ | |
typedef Grammar first; | |
typedef R second(BOOST_PP_ENUM_PARAMS(N, A)); | |
typedef typename Grammar::proto_grammar proto_grammar; | |
// Note: do not evaluate is_callable<R> in this scope. | |
// R may be an incomplete type at this point. | |
template<typename Expr, typename State, typename Data> | |
struct impl : transform_impl<Expr, State, Data> | |
{ | |
// OK to evaluate is_callable<R> here. R should be compete by now. | |
typedef | |
typename mpl::if_c< | |
is_callable<R>::value | |
, call<R(BOOST_PP_ENUM_PARAMS(N, A))> // "R" is a function to call | |
, make<R(BOOST_PP_ENUM_PARAMS(N, A))> // "R" is an object to construct | |
>::type | |
which; | |
typedef typename which::template impl<Expr, State, Data>::result_type result_type; | |
/// Evaluate <tt>R(A0,A1,...)</tt> as a transform either with | |
/// <tt>call\<\></tt> or with <tt>make\<\></tt> depending on | |
/// whether <tt>is_callable\<R\>::value</tt> is \c true or | |
/// \c false. | |
/// | |
/// \param e The current expression | |
/// \param s The current state | |
/// \param d An arbitrary data | |
/// \pre <tt>matches\<Expr, Grammar\>::value</tt> is \c true | |
/// \return <tt>which()(e, s, d)</tt> | |
result_type operator ()( | |
typename impl::expr_param e | |
, typename impl::state_param s | |
, typename impl::data_param d | |
) const | |
{ | |
return typename which::template impl<Expr, State, Data>()(e, s, d); | |
} | |
}; | |
}; | |
#undef N | |
#endif |